Light Emitting Diode (LED) lighting devices is a rapidly growing segment of lighting devices which have the advantage of offering high lumen output per energy unit due to their high efficacy. Furthermore, LED lighting devices are durable and robust which contributes to the environmental advantages of LED technology.
One of the drawbacks with conventional LED technology is that the LED as such generally emits light in a relatively narrow spectrum, thus altering the color of illuminated surfaces in comparison to the perceived color of a surface illuminated with sunlight, which is generally considered as a reference.
Various solutions have been suggested to make lighting devices based on LED technology better mimic sunlight, i.e. increasing the spectral content of the emitted light. These solutions include the use of different translucent wavelength conversion materials, through which the light generated in the LEDs is transmitted.
One embodiment proposed in US 2009/0187234 is a rotating wheel comprising a plurality of wavelength conversion materials rotated in front of a single LED at such speed that the eye integrates the individual light flashes that the wheel generates and such that no visible flicker is observed. The single LED is then perceived by the human eye as emitting light with a high frequency content comprising a mixture of the colors generated by the rotating wavelength conversion materials. US 2009/0187234 further suggests using Pulse Width Modulation (PWM) of the current to the LED for adjusting the color spectrum, and thus dimming certain frequencies.